It has been recognized that speech being projected or transmitted into a region is not necessarily intelligible merely because it is audible. In many instances such as sports stadiums, airports, public buildings and the like, speech delivered into a region may be loud enough to be heard but it may be unintelligible. Such considerations apply to audio announcement systems in general as well as those which are associated with fire safety, building or regional monitoring systems.
Relative to the latter, it has been known to conduct intelligibility testing in connection with such systems by having an installer or technician walk through a building or region being evaluated and listen to output from various speakers of the public address or alarm evacuation system to assess the intelligibility of the instructions or information being output by such devices. In an alternate mode, portable intelligibility analyzers can be carried through the building to each region of interest to provide a quantitative measure of speech intelligibility.
It also has been recognized that testing as described above requires that the installer or technician must literally move through most of the building or region being evaluated to listen or measure the intelligibility of speech signals being delivered in each region. This process is not only time consuming but expensive especially in large buildings. Additionally, when a floor or a portion of the region is being redecorated or built out for a different tenant, that portion of the building or region must be re-evaluated at additional cost of time and money after the construction and/or build-out has been completed.
It would be desirable to in some way make use of some or all of the existing equipment of such systems to improve intelligibility testing/evaluation. In such event, more frequent evaluation/testing could be conducted throughout the region or building monitored.
It also has been recognized that there is a benefit in moving from subjective evaluation of the intelligibility of speech in a region toward a more quantitative approach which, at the very least, provides a greater degree of repeatability. A standardized quantitative measure of speech intelligibility is the Common Intelligibility Scale (CIS). Various machine-based methods such as Speech Transmission Index (STI), Speech Transmission Index Public Address (STI-PA), Speech Intelligibility Index (SII), Rapid Speech Transmission Index (RASTI), and Articulation Loss of Consonants (ALcons) can be mapped to the CIS. These test methods have been developed for use in evaluating speech intelligibility automatically and without any need for human interpretation of the speech intelligibility.
In the majority of machine-based testing a noise or noise-like signal is amplitude modulated at various rates. The signal is transmitted from a source, such as a loud speaker, into a portion of a region of interest. The signals are detected, for example by an acoustic sensor. The received signals are analyzed by comparing the depth of modulation thereof with that of the test signal. Reductions in modulation depth of received signals are associated with loss of intelligibility.
Details of machine-based evaluations have been published and are available for example in “The Modulation Transfer Function In Room Acoustics as a Predictor of Speech Intelligibility” by Steeneken and Houtgast, Acustica V28, PG66-73 (1973) and “A Review of the MTF Concept in Room Acoustics and its Use for Estimating Speech Intelligibility in Auditoria” by Steeneken and Houtgast, Institute for Perception TNO, Soesterberg, the Netherlands (1984).
The above described evaluation process can be carried out by any one of a variety of publicly available analysis programs as would be available to those of skill in the art. One such program has been disclosed and discussed in an article, “The Speech Transmission Index Program is Up and Running”, Lexington Center and School for the Deaf, V3.1 (Sep. 9, 2003). Other programs for evaluating CIS-mappable intelligibility evaluation are available as would be known to those of skill in the art.
There thus continues to be on ongoing need for improved, more efficient, intelligibility testing in connection with fire safety/evacuation voice announcement systems. It would be desirable if the recognized benefits of CIS-mappable processing could be incorporated into such systems to improve intelligibility testing thereof. It also would be desirable to be able to incorporate such functional capability in a way that takes advantage of easily installable, wireless device which are intended to be distributed throughout a region being evaluated so as to minimize additional installation cost and/or equipment needs. Preferably such functionality could not only be incorporated into the devices being installed, but also could be cost effectively incorporated as upgrades to existing systems.